Focal shift of the converging spherical wavefront light diffracted by a circular aperture is numerically studied with the method of calculating the vector diffractive field by using Borgnis potentials given in Part I [J. Opt. Soc. Am. A23, 872 (2006)]. The quantitative dependence of the focal shift on the geometric parameters is discussed. The focal shift is mainly determined by the Fresnel number (N<sub>f</sub>) on the geometric focusing plane of the converging light, and an empirical formula between the fractional focal shift and the Fresnel number is deduced for N<sub>f</sub><2. The focal shift of the same geometry is also studied on the basis of the scalar Rayleigh theory of diffraction, and its comparison with and difference from the result of our method are presented.
© 2006 Optical Society of America
Diffraction and Gratings
Original Manuscript: November 11, 2005
Revised Manuscript: December 1, 2005
Manuscript Accepted: December 1, 2005
Xueen Wang, Zhaozhong Fan, and Tiantong Tang, "Numerical calculation of a converging vector electromagnetic wave diffracted by an aperture using Borgnis potentials. II. Application to the study of focal shift," J. Opt. Soc. Am. A 23, 1326-1332 (2006)